Issue #1645328 by Liam Morland, darvanen, shravan sonkar, andregp,...

Issue #1645328 by Liam Morland, darvanen, shravan sonkar, andregp, mandar.harkare, jhedstrom, sun: Add test to ensure fieldset allows any non-empty-string #title

core/modules/system/tests/modules/form_test/src/Form/FormTestGroupFieldsetForm.php

@@ -37,6 +37,10 @@ public function buildForm(array $form, FormStateInterface $form_state, $required
       '#type' => 'textfield',
       '#title' => 'Nest in container element',
     ];
+    $form['fieldset_zero'] = [
+      '#type' => 'fieldset',
+      '#title' => 0,
+    ];
     return $form;
   }
 

core/modules/system/tests/src/Functional/Form/ElementTest.php

@@ -144,6 +144,7 @@ public function testGroupElements() {
     $this->assertSession()->elementsCount('xpath', '//div[@id="edit-container"]//div[@class="details-wrapper"]//label', 1);
     $this->drupalGet('form-test/group-fieldset');
     $this->assertSession()->elementsCount('xpath', '//fieldset[@id="edit-fieldset"]//div[@id="edit-meta"]//label', 1);
+    $this->assertSession()->elementTextEquals('xpath', '//fieldset[@id="edit-fieldset-zero"]//legend', '0');
     $this->drupalGet('form-test/group-vertical-tabs');
     $this->assertSession()->elementsCount('xpath', '//div[@data-vertical-tabs-panes]//details[@id="edit-meta"]//label', 1);
     $this->assertSession()->elementsCount('xpath', '//div[@data-vertical-tabs-panes]//details[@id="edit-meta-2"]//label', 1);